The field of the invention is radio frequency resonators, and particularly, resonators employed in gyromagnetic resonance spectroscopy.
Gyromagnetic resonance spectroscopy is conducted to study nuclei that have a magnetic moment, which is called nuclear magnetic resonance (NMR) and electrons which are in a paramagnetic state which is called paramagnetic resonance (EPR) or electron spin resonance (ESR). There are also a number of other forms of gyromagnetic spectroscopy that are practiced less frequently, but are also included in the field of this invention. In gyromagnetic resonance spectroscopy, a sample to be investigated is subjected to a polarizing magnetic field and one or more radio frequency magnetic fields. The frequency, strength, direction, and modulation of the magnetic fields varies considerably depending upon the phenomena being studied. Apparatus such as that disclosed in U.S. Pat. Nos. 3,358,222 and 3,559,043 has been employed for performing such experiments in laboratories, but widespread commercial use of gyromagnetic resonance spectroscopy techniques has been limited.
The reason for the limited commercial application of gyromagnetic resonance spectrometers is their complexity and high cost. Very high radio frequencies are required for some measurement techniques (such as electron spin resonance measurements, and very strong polarizing magnetic fields are required for others (such as nuclear magnetic resonance). In addition, the physical structures for applying multiple fields to a specimen are complex, particularly when the temperature of the specimen is to be controlled, or the specimen is to be irradiated with light during the measurement.
A split-ring resonator has recently been proposed by W. N. Hardy and L. A. Whitehead for use at radio frequencies between 200 and 2000 MHz. This resonator is characterized by its uncomplicated structure, its high filling factor (magnetic energy stored in the specimen region divided by the total stored magnetic energy) and its small size. Although this proposed structure offers many advantages over prior resonators employed in gyromagnetic resonance spectrometers, it is limited at higher frequencies and it is difficult to properly apply additional magnetic fields to a specimen contained within the split-ring resonator.